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Model 5065A
Circuit Diagrams, Theory, and Maintenance
1 MHz FREQUENCY DIVIDER A6 THEORY
The A6 module uses regenerative division to divide 5
MHz to 1 MHz as shown in Number 4.
The 1 MHz output also couples to the start-circuit de
tector stage of CR5, CR6, and Q7 which sends a dc start
signal to start amplifier Q3 for automatic start action
with the START/AUTO START switch at AUTO START.
1 MHz Regenerative Divider
5MHz
T~3l
4MHz
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The 1 MHz divider is a regenerative divide-by-5 circuit
followed by an amplifier stage. This assembly includes
signal-sensing logic circuitry to control the divider-start
circuits. Assume the 5 MHz signal from A10 Oscillator
Assembly is present at the divider circuit input, but the
1 MHz output has not started. Producing the 1 MHz
output requires a 1 MHz signal at the base of X4 Multi
plier Q4 (this 1 MHz signal is derived from the output
signal once the divider starts).
Prior to divider start,
the required 1 MHz signal is obtained by converting the
tuned-amplifier circuit of Q6 into a 1 MHz oscillator by
feeding a signal from its output back to its input through
field-effect transistor Q5.
The 5 MHz signal input to A6 is amplified by Q1.
Capacitive voltage divider C5, C6 couples a portion of
Q1 output to the start-circuit detector stage of CR1,
CR2, Q2, and Q3.
With the START/AUTO-START
switch completing a signal path to Q5 base with this
switch in either position, the detector stage biases Q5
"on" to complete the feedback path for Q6 which then
oscillates at 1 MHz.
Multiplier stage Q4 converts 1 MHz at its base to 4 MHz
in its tuned collector circuit. The resulting 4 MHz mixes
with the input 5 MHz from T1 in mixing diode CR4.
The parallel resonance of L2 and C11 tuned to 1 MHz,
traps all undesired frequencies in the mixing product.
The remaining 1 MHz couples to Q6 to complete the
regenerative feedback path.
Sustained regenerative
oscillation produces 1 MHz which is amplified by Q8
and Q9. This 1 MHz output is also rectified by CR7 and
filtered by C28, R35, and C29 for a dc output to the 1
MHz position of the CIRCUIT CHECK meter.
The 1 MHz output to A4 100 kHz Frequency Divider is
coupled through C16 from Q6.
A6 MAINTENACE
NORMAL OPERATION
The A6 circuits produce 1 MHz outputs derived by re
generative division of 5 MHz.
The A6 Assembly is
placed in operation either by placing the START-AUTO
START switch in the START position, or by leaving this
switch in the AUTO START position whereupon the A6
will start divising 5 MHz when it is applied. A6 outputs
are as follows:
a. 1 MHz to front and rear 1 MHz jacks from
A6(15).
b.
Rectified 1 MHz output to CIRCUIT CHECK
meter from A6(12).
c.
1 MHz output to A4(6) from A6(9).
OPERATIONAL CHECK
a. A simple check of A6 operation can be done by
observing the CIRCUIT CHECK 1 MHz indication and
comparing it with the reference meter readings on the
front-panel door. Checking the 100 kHz meter reading
will verify that the A6 Assembly is delivering 1 MHz for
division to 100 kHz in the A4 100 kHz Frequency
Divider.
b. To check operation of the START AUTO-START
switch, set this switch at the center-off position and
momentarily disconnect A10J4. Note that with the top
cover removed, A10J4 is accessible. Without a 5 MHz
input to A6, there should be no A6 1 MHz output (or a
dc start signal to A4). With A10J4 reconnected, there
should be no 1 MHz output until the START AUTO
START switch is placed at either START or AUTO
START.
c. To verify that the 1 MHz output is within speci
fications, proceed as follows:
1)
Using the 5065A 5 MHz output as an external
time base input to a counter, connect the 1 MHz
front-panel jack to the counter and check for
1 M H z ± 1 count. Disconnect the counter.
8-38
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